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Boxing my frame

Discussion in 'The Garage' started by 72THING, Mar 3, 2004.

  1. 72THING

    72THING 1/2 ton status

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    Two weeks ago, my frame broke almost completely in half at one of my front shackle hangers for the front springs. The shackle hanger bracket inside the framerail was about the only thing keeping it together.

    For the past couple weeks I've beeen working on boxing the frame from the rear of the engine crossmember to the very end of the rear of the frame. I'm using 7/8" OD DOM tubing to sleeve the bolts through the frame where its boxed for additional strength. I'm using 1/8" diamond plate for the actual boxing and I'm also welding up all the crossmembers where they're riveted together to keep them from moving.

    I just finished one framerail and it turned out really good. I know my little Lincoln 110V wire feed welder is getting a workout. Hopefully the boxing will take most of the flex out of the frame, because that's been a big problem. I can actually feel the floorboards flex under my feet as I go over obstacles and my cab is literally splitting apart at the seams. Plus my clutch pedal is constantly changing positions and it makes me look like worse of a driver than I really am.

    Will
     
  2. Triaged

    Triaged 1/2 ton status

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    My frame cracked where the core support body mount is on the drivers side. I bought a welder this summer and patched it up. I would like to box the frame sometime but I have a bunch of other projects that need to be taken care of first.
     
  3. 84_Chevy_K10

    84_Chevy_K10 Banned

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    I personally think you're opening up a can of worms that will eventually lead to more problems.
     
  4. 72THING

    72THING 1/2 ton status

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    Why would you think that? What problems?

    Will
     
  5. 84_Chevy_K10

    84_Chevy_K10 Banned

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    [ QUOTE ]
    Why would you think that? What problems?

    Will

    [/ QUOTE ]

    The stock frame is designed to flex to a certain degree and everyone that stiffens one seems to end up with a cracked frame sooner or later.

    I am not an expert or an engineer so I'll leave it at that. I can't tell you what will result from the modification you're making other than that it's a can of worms that I personally wouldn't open. I'd let the body split at the seams before I'd stiffen a frame unless I knew EXACTLY what I was doing.
     
  6. BlueBlazer

    BlueBlazer 1/2 ton status

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    [ QUOTE ]
    everyone that stiffens one seems to end up with a cracked frame sooner or later

    [/ QUOTE ]

    Examples besides one of your buddies?
     
  7. 72THING

    72THING 1/2 ton status

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    Well I noticed that '88 and up truck frames are boxed from the front of the truck until past the transfer case, so I don't think what I'm doing will hurt anything. Also, my friend's '66 IH Scout 800 has a nice, fully boxed frame. I still expect my frame to flex, but hopefully a lot less than it used to. Since my stock frame cracked anyway, if it cracks while boxed then its really no different, but I think it will be a lot stronger. Besides, I've already got one side done so there's no backing out now.

    Will
     
  8. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    IMO, the suggestion to think carefully about boxing the frame is a good one. And I do have the personal experience to back up that statement from years of cutting, lengthening, shortening, splicing, repairing, etc. frames for a living including many extended frame working trucks. That also includes real training, not just doing it and getting away with it. I've also discussed the reasons behind this at length before but I've lost interest in continuing to pursue these discussions as it seems most people who are considering "boxing" and "making the frame rigid" are utterly convinced of the correctness of their path and there is no way to convince them otherwise.

    So, I'll just boil it down like this. In general, for most uses, I would recommend not boxing it all. If you simply feel you must, then I would say do it all to avoid most of the potential for problems. But frankly, even if done right, I don't see the benefits as worth the time and expense for the vast majority (read “nearly all”) of 4x4s. Anything in between really needs some VERY serious thought and *real* engineering to do it without creating localized stress that will eventually lead to failure. It's just a matter of time, where the length of time depends on a combination skill, luck, and usage. If you do it wrong, you just created another problem just exactly like the GM steering box issue. And like the steering box problem, it will likely take years to surface so Joe Bob thrashing one just like that for 2 years doesn’t change my opinion.

    And to put my money where my mouth is, my frame is completely stock (at least so far as what is left of it anyway) complete with factory rivets in all locations where I have not moved stuff around. Boxing and/or tying the cage to the frame in an effort to “make it rigid” has never even been considered… There are valid reasons to consider these things, but “making it rigid” is not one of them IMO.

    Good luck...
     
  9. az-k5

    az-k5 1/2 ton status

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    On a slight, but not highly, engineering approach. The boxed frame will be strong- true. The rest of the frame will be weaker. The joint of the two will be a stress riser. The truck will still try to flex the frame but instead of it being out 4" of parralles on a 118" of steel it might be 2.5" out of parrallel in only the remaining 74" (or so). This means the rest of the already weak frame might just be gettin' twisted that much more. i can't say for sure.

    The numbers used above are nowhere near exact, just simple examples to keep in mind.
     
  10. zcarczar

    zcarczar 1/2 ton status

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    Russ, say a guy boxed the entire frame, front to back completely and filled in all of the unused holes in the frame creating basically a square tube type frame. My friend did this and beats the hell out of his truck and its holding up fine, I know his last frame was a stock frame that he broke off roading. Sooo I would imagine that a more rigid frame has been a good thing for him, but you say its not a good thing for the frame to flex? Oh and the truck was in TTC this year too, the beeter.
     
  11. Triaged

    Triaged 1/2 ton status

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    ...I thought you were talking about Chris...

    I am with Russ on the all or nothing approach being the safist. As said before the point where the boxed/non-boxed meets will be a stress risor. If you look at any 1/2 boxed frames from the factory you will notice that they "fish mouth" the intersection. I also supose that alot of thought goes into where that intersection will be.

    A full boxed frame will be stronger than (and flex a bit less) than a non-boxed frame as long as it is done right. A half boxed frame could go either way...

    Oh...I think I remember Chris saying he broke 2 frames before he boxed the 3rd.
     
  12. 72THING

    72THING 1/2 ton status

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    I really appreciate everyone's insight and input on this matter. I'm gonna look into boxing the front part of the frame also, to avoid stress cracks. I realize I have no engineering background and this project was something that sounded good in my mind, since my frame had developed cracks being completely stock. Maybe '72 and down frames are weaker the '73 and up, because my friend's stock '79 frame doesn't flex near as bad as mine does.

    I talked to Stephen Watson after I started the boxing and he said it will definitely make the frame stronger but was a pain in the butt and that most people wouldn't want to spend the time to do it. Oh well, I'm just gonna take my time and think things through carefully.

    Will
     
  13. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    First off, let me apologize. Looking back at it, my post sounds a little harsh but that was not my intent. Late, aggravated at unrelated things, and a historically troublesome topic... Sorry...

    In any case, Matt and Dan are dead on with what I was talking about. And as Dan said, where the transition occurs is very important. Some time back I wrote a very long and detailed explanation of my views and experience with frame modification and I've jumped in a few times with short descriptions like they both posted. Unfortunately each time multiple people jumped in with "so-n-so" did "this-n-that" and it held up great... So, I've petty much taken to avoiding these posts. Seems boxing a frame and/or making it more rigid is a almost a religious thing for some. I will say this, though I'm not a mechanical engineer (or related), I've got more frame mod/repair experience and training than most of those doing these "frame strengthening" exercises, and I'm not at all convinced I could do a partial boxed frame correctly (a relative term in this case). So I generally advise anyone to avoid it...

    And Stephen definitely knows what he is talking about, and I'm not saying he is wrong. The boxed section will be stronger if done competently, the issue is with what happens at the transition. Deep fish-mouthing is VERY important in this case, and the worst would be the typical abrupt termination. The transition is also often right around the fire wall, which is also about the worst place to put it.

    Jason, that's why I said box it all if your going to box. It avoids most of the pitfalls people get into with boxing part of the frame. As far as filling in the holes, don't bother, it's not worth it for all those holes unless you want it to look slick (hot roders do this). We're talking (estimating) far less than 1% stronger and that's assuming all the holes were filled correctly. Think about "speed holes" on race cars... and the holes in the frame are generally pretty small. Those little holes are not going to hurt you... As for the previous broken frame, I’ll bet dollars-to-donuts it broke because of either impact damage (repaired or not) or modifications like a roll bar frame tie in (which creates frame spans that work against each other).

    Here’s a kicker for you. When you have the flexy frame tear apart the body, are you running poly body mounts? Body lifts? If you break an unmodified frame, are you running the above with a strong cage the makes the body rigid? Even these things come into play because they are not as flexy as the stock body mounting system so you are created localize regions that do not move as they were *engineered* to do. Sure, you can damage the body with frame flex on stock mounts (especially in trucks where the bed can hit the cab, but generally not on short beds with good stock body mounts), but it’s really not very likely (or severe) in my experience. A rigid body (generally due to body mounted cage) combined with poly mounts will sometimes rip the body mount brackets right off the frame. If/when those are strengthened, you have the same behavior as mounting the cage to the frame, localized stress risers. Not that your not gaining something in mounting the cage to the frame (another of those “main stream” fixations that I don’t subscribe to, but that’s another contentious thread) but as with most mods, there are trade offs, and this one is not different. Same thing with my preferred sub-frame style cage mounts, if you run poly it plays hell on the body mount frame brackets. That’s why I collect and run stock rubber donuts with no lift pucks. I do have poly in my son’s truck, but that’s a different set of trade offs and will change if I can ever find a good set of the old style stock rubber mounts.

    Arghhh, that’s why I stay off these threads most of the time… I invariably waste too much time explaining (evangelizing?) my views. /forums/images/graemlins/laugh.gif Good luck with whatever you try.
     
  14. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Oh, and one more thing, a ladder frame *will* still flex even if boxed, it just won't flex as much. That's what ladder frames do... To stop the flex (or rather reduce it to negligible proportions) you would have to transition to a space frame which triangulates in 3 dimensions. At that point you’re moving into buggy/truggy land…
     
  15. BlazerGuy

    BlazerGuy 3/4 ton status

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    [ QUOTE ]
    I invariably waste too much time explaining (evangelizing?) my views.

    [/ QUOTE ]
    I, for one, appreciate it. /forums/images/graemlins/bow.gif
     
  16. MoonMan

    MoonMan Registered Member

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    Boxing the frame rails will not eliminate frame flex. The manner in which the frame rails flex is based mainly on the cross members and their associated connections to the frame rails. By boxing the frame rails you help to elimate twist of the rails by creating a symmetric section (though rectangular which is not the optimal shape) that is much stiffer in torsion than the original channel frame.

    The use of rivets holding the frame together is cheaper and easier at a manufacturing level, but at a structural level it also creates a connection that is fully engaged about the circumfrence of the hole. This means that there is no slop in the connection (when new, disregarding wear) that does not allow movement of the frame relative to the cross members. By boxing the frame on a 30+ year old truck you eliminate the torsion of the rails and increase the force on the connections. The connections inevitably through their cycle life loosen, which in this case can often cause failure.

    Therefore, to effectively limit the flexing of you frame you will not only need to box the frame, but increase the size and connection capacity of the cross members. As BadDog stated, the only way to totally eliminate frame flex is by increasing the depth of the frame dramatically, i.e. a 3 dimensional cage.

    To give you some advice, which i hesitate to do, I would box the frame (on both frame rails) at the area of fracture to reinforce it. You will not eliminate frame flex by boxing the frame rails alone, but by strengthing the entire ladder frame. I would examine the riveted connections for play (which I expect) and repair them with 7/16" grade 8 bolts.

    BTW, filling in the holes along the web of the frame will only increase the shear strength of the frame, not limit flex.
     
  17. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Good point on the rivets (something else that many people deride without having a clue). I just assumed (yeah, I know...) that anyone going to the trouble of boxing the frame would weld up the rest as well. Thanks for filling in the oversight...
     
  18. 84_Chevy_K10

    84_Chevy_K10 Banned

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    [ QUOTE ]
    [ QUOTE ]
    everyone that stiffens one seems to end up with a cracked frame sooner or later

    [/ QUOTE ]

    Examples besides one of your buddies?

    [/ QUOTE ]

    Don't need examples. Read above and think about the engineering of this project. It doesn't take a rocket scientist to realize that if you stiffen it, it may crack. As stated above, frames are designed to flex, and I'm not the only one who believes that stiffening a frame can lead to problems.

    Taking the risk of sounding harsh, I'm simply going to tell you, Tyler, that you don't always have to do something stupid, realize what you did was a bad idea, and start over with a more intelligent idea in this sport. It's perfectly acceptable to use your brain to decide if such a project would be a good idea or not. To me, I wouldn't spend the time, for the very reasons set apart above.

    I'm not an engineer, but I aspire to be one, either amateur or professional one day. Fourwheeling is my way of getting to let this out and part of the reason I enjoy it so much. It's just like when I moved my shackle hangers last week--sometimes it's not about your experience, but more about thinking about what works and what doesn't, and modifying your truck accordingly.
     
  19. 72THING

    72THING 1/2 ton status

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    First, to Russ, you didn't sound harsh at all. I WANT to hear your opinion, experience, and advice. No need to apologize. I realize this project would create some controversy and my lack of any engineering background may prove to be interesting to say the least. I am also running poly mounts, but only because they were so much cheaper than the factory rubber ones. I'm gonna try to get my hands on some stock ones because I have killed a couple of my body mount brackets already.

    To Moonman, you have some very good points. I have either drilled out my crossmember rivets and replaced them with graded 7/16" bolts, fully welded the crossmembers to the framerails, or both. I'm fully boxing both framerails and also some of the c-shaped factory crossmembers. I'm planning on adding some additional crossmembers to help tie the framerails together. I don't expect to eliminate frame flex, just reduce it some.

    Will
     
  20. 84_Chevy_K10

    84_Chevy_K10 Banned

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    If I knew enough to do this correctly, I'd be doing it. Don't get me wrong, I don't think it's a stupid idea, just that it takes more brains than I've got to do it correctly.
     

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